JPH08272466A - Semiconductor device - Google Patents

Abstract

(57) [Summary] [Configuration] A semiconductor device having a power supply switching circuit and a step-down power supply circuit. The step-down circuit 100 and the internal circuit 102 are directly connected, and the MOS transistor 101 is interposed between the power supply VDD and the internal circuit 102. Switch 101 is off
In this case, the internal circuit operates with the step-down power supply supplied from the step-down circuit. When the power supply VDD is used as the power supply for the internal circuit, the MOS transistor of the switch 101 is turned on. At this time, since the step-down power supply is also connected to the power supply VDD, a power supply short circuit occurs between the step-down power supply and VDD. In order to avoid this, the transistor of the step-down circuit output section is turned off.
FF is used so that the step-down power supply is in a high impedance state. [Effect] The usable power supply voltage range of the step-down power supply is expanded,
Low power consumption can be achieved. In addition, the power source of the internal circuit is the power source V
When the voltage is set to DD, the voltage drop of the switch 101 is hardly affected because the back gate effect does not occur.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply switching circuit and a step-down power supply circuit in an IC.

[0002]

2. Description of the Related Art A conventional step-down power supply circuit always outputs a stepped-down voltage regardless of the state of a power supply switching circuit. In addition, the conventional power supply switching circuit, as shown in FIG.
The MOS transistor 111 is interposed between the step-down power supply circuit 110 and the internal circuit 113 and is affected by the voltage drop in the MOS transistor section. Furthermore, since the sub of the MOS transistor 111 is connected to VDD, M is affected by the back gate effect of the MOS transistor.
The Vth of the OS transistor 111 becomes large, and there is a large effect of further voltage drop. Further, in the MOS process, Vth varies, which also has an effect.

[0003]

As described above, in the conventional power supply switching circuit, the MOS transistor is interposed between the step-down power supply and the internal circuit power supply line.
The voltage drop in the OS transistor portion is remarkable, and the power supply voltage supplied to the internal circuit is considerably lower than the step-down power supply voltage. The power supply voltage at which the internal circuit operates is determined by the integrated circuit, and the power supply voltage that can be used by the step-down power supply is, for example, 1 / n step-down, (the minimum operation voltage of the internal circuit) × n.
+ (Voltage drop by MOS transistor) ΔV × n or more. Normally, the power supply voltage of the IC is fixed, and the wider the voltage range in which the step-down power supply can be used, the lower the power consumption of the IC. The conventional power supply voltage switching circuit has a problem that the voltage range in which the step-down power supply can be used is narrowed by ΔV × n, and the power consumption of the IC cannot be reduced. Further, when the step-down power supply and the internal circuit power supply line are directly connected without the MOS transistor 111 shown in FIG. 3 interposed between the step-down power supply and the internal circuit power supply line, the conventional step-down power supply circuit is always stepped down. Since the voltage is output, there is a new problem that the power source is short-circuited with the power source of the IC.

[0004]

According to the present invention, there is provided a semiconductor device comprising:
A step-down circuit that steps down the power supply voltage, an output voltage of the step-down circuit, an internal circuit that operates by selecting one of the power supply voltages, and a switch provided between the output terminal of the step-down circuit and the power supply voltage. And the switch is a MOS transistor, the MOS transistor is controlled by the internal circuit, and when the switch is conductive, the internal circuit sets the output terminal of the step-down circuit to a high impedance state.

[0005]

1 shows a circuit diagram of a power supply switching circuit as a first embodiment of the present invention.

In FIG. 1, at node 103, an internal circuit power supply line, a step-down power supply output section, and a power supply switching MO.
The S transistor 101 is connected. When the internal circuit operates with a step-down power supply, the MOS transistor 10
1 is turned off, and the power supply VDD and the step-down power supply are separated. As a result, the internal circuit operates with the power supply supplied from the step-down circuit. Compared with FIG. 3 of the conventional circuit, the conventional circuit uses two power supply switching MOS transistors 111 and 112. The sub-potential of the MOS transistor 111 must be connected to VDD. This is shown in FIG. 5, the MOS transistor 111 of FIG.
A description will be given based on the sectional view of the IC 112. Two MO
The drains 162 and 164 of the S transistors are the nodes 16
Since it is connected at 0, VDD is used as the internal power supply.
, The gate 167 is turned on, and the drain common portion of the node 160 becomes VDD voltage. This gives 16
When the sub-potential of the MOS transistor 6 is set to the stepped-down power supply voltage, a current flows from the drain 164 to the sub 166 through the forward diode. 166 as shown in FIG.
If the sub of the MOS transistor is connected to VDD, current does not flow because the drain 164 and the sub 166 have the same potential. However, when the potentials of the source 163 and the sub 166 are different, a back gate effect occurs in the MOS transistor, and the voltage drop due to the MOS transistor 111 shown in FIG. Also, the MOS transistor is
Since Vth varies due to the MOS process, Vth
If it is large, the step-down power supply cannot be used at all. Therefore, in the circuit of the present invention in which the MOS transistor 111 shown in FIG. 3 is eliminated between the step-down power supply and the internal circuit power supply line, all the above problems can be solved. Next, power supply V
When the DD is used as the power source of the internal circuit, the MOS transistor 101 shown in FIG. 1 of the present invention is turned on,
The power supply line of the internal circuit is VDD. Since the step-down power supply is also connected to the power supply VDD, a power supply short circuit occurs between the step-down power supply and VDD. This must be avoided. For example, the output stage of the 1/2 step-down circuit is composed of a circuit as shown in FIG. Operation is initially transistor 120, 1
22 is turned on, and transistors 121 and 123 are turned off
are doing. As a result, the capacitors 124 and 125 are connected in series. In the next step, transistors 120 and 12
2 turns off and 121 and 123 turn on. As a result, the capacitors 124 and 125 are connected in parallel. By repeating this in a certain cycle, the node 126
A voltage (1/2 VDD) that is stably stepped down by 1/2 is output to. When the power supply VDD is connected to the node 126, the power supply is in a short circuit state, and a useless current always flows to VSS via the capacitor. Therefore, in the present invention, when the power supply of the internal circuit is set to VDD, the transistors 120 and 123 in FIG. 4 are turned off, the transistors 120 and 122 are turned off, the transistors 121 and 123 are turned off, or the transistor 121,
122 is turned off, or the transistors 120, 121,
All 122 and 123 are turned off so that the step-down power supply is in a high impedance state. The instruction to the step-down circuit to be in the high impedance state is given by an internal circuit, a LOW level signal is output to the control line of the node 105 shown in FIG. 1, and the step-down circuit, for example, transistors 121 and 123 are always turned off. Let As a result, the output terminal of the step-down circuit is in a high impedance state, and it is possible to avoid a short circuit with the power supply VDD.
When using the power supply VDD as the power supply for the internal circuit,
FIG. 1 interposed between the power supply VDD and the internal circuit power supply line
Although there is an influence of the voltage drop of the MOS transistor 101, there is no influence of the back gate effect. Therefore, the influence of the voltage drop can be almost eliminated only by increasing the drive capability of the transistor. Example In FIG.
This is an example of using one step-down circuit, but the same applies when a plurality of step-down circuits are used. FIG. 2 shows a circuit diagram of a power supply switching circuit when a plurality of step-down circuits are used as a second embodiment of the present invention. In the case of FIG. 2, when the power supply VDD is used as the power supply of the internal circuit, both the step-down circuits (1) and (2) are in a high impedance state. In addition, each step-down circuit uses, for example, a step-down circuit (1) in order to eliminate a power supply short circuit between the step-down circuits.
Step-down circuit (2) when used as a power source for internal circuits
Becomes a high impedance state. In the above-mentioned embodiment, the power supply VDD and the P-channel MOS transistor are used for explanation, but the power supply VSS and the N-channel MOS are used.
The same applies when a transistor is used.

[0007]

As described above, according to the present invention, the step-down power supply circuit is used, and the step-down power supply output by the step-down power supply circuit and the power supply of the IC are switched to each other. The power supply voltage range that can be expanded is widened and low power consumption can be achieved. This is very effective when the 1 / n step-down power supply is used, because the power consumption is 1 / n compared to when the IC power supply is used. In particular, when a battery or the like is used, the output voltage of the battery gradually decreases with use time. Therefore, the wider the power supply voltage that can be used by the step-down circuit, the longer the battery can be used. Therefore, according to the present invention, it is possible to maximize the advantage of using the step-down circuit, that is, to reduce the power consumption of the IC.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a power supply switching circuit showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a power supply switching circuit showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a power supply switching circuit showing a first conventional example.

FIG. 4 is a circuit diagram of a step-down circuit output section showing a first embodiment of the present invention.

FIG. 5 is an IC cross-sectional view of a transistor portion of a power supply switching circuit showing a first conventional example.

[Explanation of symbols]

100, 110, 200, 207 Step-down circuit 102, 113, 202 Internal circuit 101, 111, 112, 120, 121, 122, 1
23, 201 MOS transistors 124, 125 capacitors 104, 116, 117, 127, 128, 129, 1
30, 167, 168, 204 MOS transistor gate 161, 163 MOS transistor source 162, 164 MOS transistor drain 106, 118, 119, 165, 166, 169, 1
70, 206 MOS transistor sub 171 IC substrate portion 172 Step-down power supply voltage 103, 105, 114, 115, 126, 131, 1
32, 160, 203, 205, 208 Connection node

Claims (3)

[Claims] 1. A step-down circuit that steps down a power supply voltage, an output voltage of the step-down circuit, an internal circuit that operates by selecting one of the power supply voltage, and an output terminal of the step-down circuit and the power supply voltage. A semiconductor device having a switch provided in. 2. The semiconductor device, wherein the switch is a MOS transistor, and the MOS transistor is controlled by the internal circuit. 3. The semiconductor device according to claim 1, wherein the internal circuit sets an output terminal of the step-down circuit in a high impedance state when the switch is turned on.